This section provides background information related to the present disclosure which is not necessarily prior art.
One common type of evaporator for cooling systems is a fin-and-tube evaporator having one or more refrigerant circuits that are fin-and-tube cooling coils. Each refrigerant circuit has tubes that extend back and forth between opposed sides of the evaporator with fins affixed to the outside of the tubes. The tubes are fluidly coupled together, end to end. Refrigerant flows through the tubes and air to be cooled flows across the fins and outside of the tubes.
These evaporator coils can have various configurations, such as an A coil, V coil and slab coil. A slab coil configuration as the name implies has the configuration of a slab with the tube (or tubes) running back and forth across the slab with fins affixed to the outside of the tubes. A coil and V coil configurations typically have two slab coils arranged in an A or V configuration.
In a slab coil having a tall, relatively narrow configuration, air flow distribution across the slab coil as air to be cooled flows across it is less than optimum. The airflow face velocity of the air contacting the slab coil farthest from the air moving unit (such as a blower) used to blow the air across the slab coil is considerably reduced compared to the airflow face velocity of the air contacting the slab coil closest to the air moving unit which causes a wide variation in coil circuit temperatures. This results in lower coil capacity and lower efficiency of the system. One way of mitigating this effect is by the addition of more refrigerant tubes to the refrigerant circuits that are in the area of the lower airflow. A refrigerant circuit in this context is a plurality of tubes extending across the slab that are fluidly coupled together end to end to provide a continuous, serial refrigerant flow path through the tubes. A refrigerant circuit may for example have twelve such tubes with an inlet end of a first tube in the refrigerant circuit coupled to a refrigerant distributor and an outlet end of a last tube in refrigerant circuit fluidly coupled to a suction line. The coupled together tubes thus extend in a serpentine path back and forth across the coil slab. When the evaporator has a fin-and-tube evaporator coil configuration, each refrigerant circuit is a fin-and-tube coil with the tubes of the refrigerant circuit extending through fins that surround and contact the outer sides of the tubes. However, it is difficult to achieve good coil circuit distribution even by adding more refrigerant tubes in the area of lower airflow. The difficulty is that to add tubes to cold refrigerant circuits, tubes need to be removed from warmer refrigerant circuits since the height of the coil slab is limited. This can become an iterative process with less than desired results since multiple circuits are affected when adding/removing tubes from each. When there is a variation in coldest to warmest refrigerant circuit temperatures of more than 10° F., performance and system efficiency are less than optimal.